From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id 2B09F6B008C for ; Thu, 17 Sep 2009 18:44:40 -0400 (EDT) Received: by mail-yx0-f180.google.com with SMTP id 10so656606yxe.12 for ; Thu, 17 Sep 2009 15:44:44 -0700 (PDT) From: Nitin Gupta Subject: [PATCH 2/4] send callback when swap slot is freed Date: Fri, 18 Sep 2009 04:13:30 +0530 Message-Id: <1253227412-24342-3-git-send-email-ngupta@vflare.org> In-Reply-To: <1253227412-24342-1-git-send-email-ngupta@vflare.org> References: <1253227412-24342-1-git-send-email-ngupta@vflare.org> Sender: owner-linux-mm@kvack.org To: Greg KH Cc: Andrew Morton , Pekka Enberg , Ed Tomlinson , linux-kernel , linux-mm , linux-mm-cc List-ID: Currently, we have "swap discard" mechanism which sends a discard bio request when we find a free cluster during scan_swap_map(). This callback can come a long time after swap slots are actually freed. This delay in callback is a great problem when (compressed) RAM [1] is used as a swap device. So, this change adds a callback which is called as soon as a swap slot becomes free. For above mentioned case of swapping over compressed RAM device, this is very useful since we can immediately free memory allocated for this swap page. This callback does not replace swap discard support. It is called with swap_lock held, so it is meant to trigger action that finishes quickly. However, swap discard is an I/O request and can be used for taking longer actions. It is preferred to use this callback for ramzswap case even if discard mechanism could be improved such that it can be called as often as required. This is because, allocation of 'bio'(s) is undesirable since ramzswap always operates under low memory conditions (its a swap device). Also, batching of discard bio requests is not optimal since stale data can accumulate very quickly in ramzswap devices, pushing system further into low memory state. Links: [1] http://compcache.googlecode.com/ Signed-off-by: Nitin Gupta --- include/linux/swap.h | 5 +++++ mm/swapfile.c | 34 ++++++++++++++++++++++++++++++++++ 2 files changed, 39 insertions(+), 0 deletions(-) diff --git a/include/linux/swap.h b/include/linux/swap.h index 7c15334..64796fc 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -8,6 +8,7 @@ #include #include #include +#include #include #include @@ -20,6 +21,8 @@ struct bio; #define SWAP_FLAG_PRIO_MASK 0x7fff #define SWAP_FLAG_PRIO_SHIFT 0 +typedef void (swap_free_notify_fn) (struct block_device *, unsigned long); + static inline int current_is_kswapd(void) { return current->flags & PF_KSWAPD; @@ -155,6 +158,7 @@ struct swap_info_struct { unsigned int max; unsigned int inuse_pages; unsigned int old_block_size; + swap_free_notify_fn *swap_free_notify_fn; }; struct swap_list_t { @@ -295,6 +299,7 @@ extern sector_t swapdev_block(int, pgoff_t); extern struct swap_info_struct *get_swap_info_struct(unsigned); extern int reuse_swap_page(struct page *); extern int try_to_free_swap(struct page *); +extern void set_swap_free_notify(struct block_device *, swap_free_notify_fn *); struct backing_dev_info; /* linux/mm/thrash.c */ diff --git a/mm/swapfile.c b/mm/swapfile.c index 74f1102..b165db0 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -554,6 +554,38 @@ out: return NULL; } +/* + * Sets callback for event when swap_map[offset] == 0 + * i.e. page at this swap offset is no longer used. + */ +void set_swap_free_notify(struct block_device *bdev, + swap_free_notify_fn *notify_fn) +{ + unsigned int i; + struct swap_info_struct *sis; + + spin_lock(&swap_lock); + for (i = 0; i <= nr_swapfiles; i++) { + sis = &swap_info[i]; + if (!(sis->flags & SWP_USED)) + continue; + if (sis->bdev == bdev) + break; + } + + /* swap device not found */ + if (i > nr_swapfiles) { + spin_unlock(&swap_lock); + return; + } + + BUG_ON(!sis || sis->swap_free_notify_fn); + sis->swap_free_notify_fn = notify_fn; + spin_unlock(&swap_lock); + return; +} +EXPORT_SYMBOL_GPL(set_swap_free_notify); + static int swap_entry_free(struct swap_info_struct *p, swp_entry_t ent, int cache) { @@ -585,6 +617,8 @@ static int swap_entry_free(struct swap_info_struct *p, swap_list.next = p - swap_info; nr_swap_pages++; p->inuse_pages--; + if (p->swap_free_notify_fn) + p->swap_free_notify_fn(p->bdev, offset); } if (!swap_count(count)) mem_cgroup_uncharge_swap(ent); -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org